We have shown that a latent infection of herpes simplex virus type 2 (HSV-2) can be established in a human neuroblastoma cell line IMR-32 if the infected cells are cultured at 40 degrees C. In the present study, viral polypeptides and cellular heat-shock proteins which were synthesized in HSV-2 infected IMR-32 cells cultured at 40 degrees C were analyzed by polyacrylamide gel electrophoresis. It was found that the synthesis of late viral polypeptide ICP 5 was markedly reduced in the infected cells at 40 degrees C as compared with those at 37 degrees C. Although infection of IMR-32 cells with HSV-2 at 40 degrees C resulted in shutoff of cellular protein synthesis, it was found that some cellular heat-shock proteins (90, 72 and 70 kd polypeptides) were synthesized and accumulated intracellularly. These findings suggest that modification of cascade regulation of HSV-2 polypeptide synthesis and/or accumulation of heat-shock proteins may be involved in the incomplete arrest of virus growth and in survival of the infected cells, leading to the establishment of HSV-2 latency in IMR-32 cells.

We have examined by immunofluorescent antibody staining technique the expression of herpes simplex virus type 1 (HSV-1) in organ cultures of the normal human oral mucosa. The expression of HSV-1 antigen was found selectively in the epithelial cell layers in relatively undifferentiated states such as basal layer and lower prickle cell layer in addition to the basement membrane. When the epithelial cells dissociated from the oral mucosa were infected with HSV-1 and association of the HSV-1 expression with the cellular differentiation was examined, the epithelial cells containing laminin in an undifferentiated state were permissive for the expression of HSV-1 antigen whereas terminally differentiated epithelial cells with the cornified envelope did not express HSV-1 antigen. These findings indicate that the expression of HSV-1 antigen is restricted in the mucosal epithelial cells in a differentiated state, although the possibility that the cornified envelope might protect the cells from infection is not excluded.

Human neuroblastoma (IMR-32) cells were infected with herpes simplex virus type 2 (HSV-2) at a multiplicity of infection (MOI) of 2 plaque-forming units (PFU)/cell and were cultured at 40 degrees C for 14 days. Then neither infectious virus particles nor virus capsids were detected in these cells whereas the presence of virus-specific antigens was observed by immunofluorescent antibody staining technique in 16.9 +/- 3.2 per cent of the infected cell population. When the cultivation temperature was shifted down from 40 degrees C to 35 degrees C, reactivation of virus growth occurred after lag periods of 2-9 days. These findings indicate that the IMR-32 cells can be latently infected with HSV-2 at 40 degrees C and that virus growth may be inhibited at the level of synthesis of virus-specific macromolecules or at some step preceding nucleocapsid formation.

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